Separating gas mixtures



Jan. l5, 1957 G. T. sKAPERDAs SEPARATING GAS MIXTURES 2 Sheets-Sheet 1 Original Filed Aug. 29, 1946 Jan. l5, 1957 G. T. sKAPl-:RDAS

SEPARATING GAS MrxTuREs original Filed Aug. 29, 194e 2 Shee'cs-Sheecl 2 ATTORNEY United States .Patent SEPARATING GAS MIXTURES George T. Skaperdas, Flushing, N. Y., assigner to The M. W. Kellogg Company, Jersey City, N. I., a corporation of Delaware Continuation .of application Serial No. 693,799, August This application April 13, 1953, Serial No.

16 Claims. (Cl. 62-123) This invention relates to an improved method and apparatus for the separation of gas mixtures containing lower and higher boiling components and other components which boil or sublime at still higher temperatures. in a more specic aspect it relates to a continuous method for the separation of air by liquefaction and rectification under moderate super-atmospheric pressure into a substantially pure oxygen-containing fraction and to the elimination of undesirable impurities, such as water, carbon dioxide or other higher boiling components, from the air before the liquefaction and rectication steps.

This application is a continuation of the inventors copending application Serial No. 693,799, filed August 29, 1946, now abandoned.

The separation of low boiling gas mixtures, for example, air and normally gaseous hydrocarbons, into relatively pure components has been accomplished by processes involving liquefaction and rectification and in such processes it has been customary to elevate the pressure and cool the gas mixture before liquefaction and rectification by counter-current cold exchange with the backward-returning products of the separation under relatively low pressure. This cold exchange causes condensation and/or solidiiication of higher boiling components present as impurities in the gas mixtures and, to prevent excessive fouling of the cold-exchange zone by accumulation of these components, it has been customary to remove them as effectively as possible. The removal has been effected by a chemical treatment of the gas mixtures before cooling or by passing the gas mixtures through the cold-exchange zone until an appreciable amount of the higher boiling components has accumulated in the apparatus and then removing the fouled apparatus from the process for a thawing out procedure. In one continuous process that does not resort to a segregated thawing out procedure, regenerators, operating in a reversing cycle, have been employed in the cold-exchange Zone. To prevent excessive fouling of these regenerators with accumulations of higher boiling components of the gas mixture, the higher boiling components have been evaporated during the reversed phase of the reversing cycle into a greater mass of the returning cold product than the mass of cornpressed gas mixture from which they were initially obtained. This requires that provision rnust be made for returning enough of the cold product during the reversed phase of the cycle to compensate for the difference in temperatures and pressures of the flowing streams. One expedient for supplying an excess of the returning product has been to purify a separate part of the gas mixture by chemical treatment, thereafter to compress the purified gas to a relatively high pressure and then expand it into the system at a point subsequent to the cooling of the main gas stream. The expansion from the higher pressure supplies additional cold and, While the method does prevent excessive fouling in the cooling step for extended periods of time, the expedient requires a combination of steps for purifying and cooling the total gas mixture and for this reason is not the most economical procedure.

lt is an object of the present invention to modify the iiow of gases in a reversing heat exchange zone combined with a mixing Zone and a separating zone so as to provide for complete removal of higher boiling components from the feed gas mixture without having recourse to chemical purification.

The present invention is equally applicable to cold exchange steps comprising either reversing cold regenerating or reversing cold-exchange zones of the non-regenerative type. In the following further description the invention is described by reference to a continuous process for the separation of air under moderate super-atmospheric pressure wherein the cooling step utilizes a countercurrent, reversing, cold-exchange zone of the non-regenerative type. It is to be understood, however, that this description presents a specific embodiment of the invention for the purpose of illustration and that the invention is capable of other embodiments and is equally applicable to the separation of other gas mixtures, such as low molecular weight hydrocarbons.

A cold exchange zone of the non-regenerative type as herein described for the separation of air accomplishes cold exchange by counter-currently passing air and a backward-returning product of the separation, such as the nitrogen-rich product, alternately through at least two duplicate passageways in the apparatus. These passageways preferably are packed with a metallic packing material of high thermal conductivity so installed as to expose an abnormally great surface area of metal to the streams of flowing gases. Wherever the metal packing touches the walls of the passageways a metal to metal bond is established to effect a highly eliicient path of thermal flow between the metal packing and the walls of the passageways. As a result of the great surface area of metal there is a rapid pick up and dissipation of heat from and to the gas streams which, combined with the efficient path of thermal flow between the passageways, ensures that heat removed from one ilowing gas stream is very eiectively transferred to the opposite flowing stream. Consequently, when the counter-currently owing streams of air and cold product are periodically switched, i. e., alternated or reversed with each other, the temperatures of the gases at all points throughout each passageway quickly assume the conditions existing in the opposite passageway at the moment of switching with no substantial temperature lag in the heat exchange relation between the two streams by reason of interchanging their channels of liow. In other words, substantially no regenerative effect is obtained in the system because of the switching. Other products of separation similarly may be passed through other passageways of the aforementioned coldexchange zone and thereby augment the cold being imparted to the incoming air. These products, however, are not necessarily passed through reversing passageways and pure products preferably are not so passed.

During the operation of the cold-exchange zone each of the reversing passageways alternately carries air, laden with higher boiling components as impurities, such as water and carbon dioxide, for half of the reversing cycle, the amount being a function of the pressure and temperature of the air. Because these components have relatively high boiling points in comparison with air, they are condensed as liquid or precipitated as a solid on the surfaces of the metal packing and on the walls of the passageway while the air is being progressively cooled. That part of the cold-exchange zone wherein such condensation or precipitation occurs may be designated as a colder portion of the zone for the purpose of definition in this specilication. Subsequently, when the passageways are alternated, that is, during the reversed half of the cycle, and when the effluent cold product has replaced the air in a passageway, these components are evaporated into the product stream and thereby are removed from the system.

Complete evaporation of these components, however, does not occur unless conditions influencing complete evaporation are effectively maintained at the points in the cold-exchange zone where depositions of such components take place. It is weltlknown that a decrease in pressure results in a gas having greater ability to carry vapors of a higher boiling, or condensable, component. Likewise, it is also well known that a decrease in temperature causes a decrease in the amount of such condensable component that can be so held in the vapor state. For example, consider a point in the cold-exchange zone where deposition of a higher boiling component of the air, such as carbon dioxide has occurred. The fact that the effluent product passing over that point is at a lower pressure than the compressed air makes it possible for the product I.to evaporate and carry away more of the carbon dioxide than the air can deposit at that point. But, as the result of the lower temperature of the efuent, it is unable to evaporate and carry away as much carbon dioxide as the compressed air deposits. Thus, it can be seen that two opposing influences determine the evaporating eiciency of a reversing cold-exchange zone. That is, the pressure differential between the compressed air and the etlluent product aids evaporation but the temperature difference hinders evaporation. Since the pressure diler ential is fixed by `the refrigeration and the distillation re quirements of the system, it becomes evident that there must be a certain critical temperature differential for any given pressure differential which can not be exceeded if complete evaporation of the carbon dioxide is to be obtained. By reason of the vapor pressure relationships involved in a system of this character this critical teml perature differential varies to a small extent from one end of the cold-exchange zone tto the other as the temperature level therein varies. The critical temperature differential also may be defined as being the maximum allowable temperature diierence.

In a reversing cold-exchange zone, wherein the compressed inflowing air is cooled by cold exchange relation with an equal mass of eliuent products, the temperature difference between the compressed air and eiuent scavenging `stream with which the air is reversed normally increases `from the warmend towards. the cold end of the cold-exchange zone. ln such a co-ld exchange relation while the existing temperature difference is suiciently below the critical temperature difference for the evaporation of the deposits at the Warm end of the exchanger, the aforementioned increase causes the temperature difference to exceed the critica] temperature dilerence for the deposited material at the cold end of the coldexchange zone, thereby making complete evaporation at the cold end impossible. This temperature difierence increases towards vthe cold end of a cold-exchange zone in which the mass of the compressed air is equal to the mass of the efliuent stream because the speciiic heat of kthe warm air stream is higher than the specific heat of the cold eluent stream as a result of the higher pressure of the former. The effect of a higher specific heat can be overcome by decreasing the mass of compressed air relative 4to the mass of effluent products in cold exchange with the air. When the mass of compressed air is reduced sufficiently, the tendency of the higher specific heat of the air to cause an increase in the temperature difference towards the cold end of the cold-exchange zone is overcome and indeed reversed so 'that the temperature difference decreases towards the cold end of the zone. By this means, it then becomes possible to decrease the temperature difference suflciently in the colder portions of the cold-exchange Zone so that Ithis, difference is smaller than the critical temperature difference. When this is accomplished, the deposited materials can be completely evaporated during the reversing cycles and the cold-exchange zone made completely operable for long periods of time.

One embodiment of this invention is concerned with the decrease of the temperature difference in the colder portions of lthe cold-exchange zone to values within the maximum allowable, 0r critical, temperature difference for carbon dioxide evaporation. This is accomplished by diverting a minor portion of the air around the colder par-t of the cold-exchange zone and, in doing this, to further reduce the temperature of the compressed air in the colder portions substantially below that temperature which would be obtained normally in the absence of any such diversion. This further reduction of the temperature of the undiverted ,air precipitates enough carbon dioxide in the colder portion so that the cold air as it subsequently leaves the cold-exchange zone is substantially devoid of this material. The two separated streams are thereafter commingled and the low temperature of the undiverted portion reduces the temperature of the diverted portion sulciently so that the carbon dioxide constituent of the latter portion substantially completely precipitates and is readily extracted therefrom by filtration or other means of removal. Pursuant to this method the carbon dioxide content of the main portion of air is deposited in the reversing cold-exchange zone and it is only a relatively small amount of this material which is discarded in the removal step.

The accompanying drawing is an exemplary process flow arrangement depicting a low presure air separation process which embodies the present invention. Referring to the drawing, atmospheric air, which has been treated previously to remove dust, water, or other impurities, and pressured to about 85 pounds per square inch gauge, is introduced into the process vthrough line 1 at a temperature of about 100 F. Line 1 connects with reversing valve 2 which has settings to permit passage of the air into reversing exchanger 3 by way of either line 4 or line S. Exchanger 3 is shown herein, for convenience, as being constructed of a number of concentric annular passage-` y iilled with a metallic packing such as a coil of edge-wound metallic ribbon, pins, etc., adxed Ito the walls thereof with a metal to metal bonding material, for example silver solder, so as to provide an extremely ecient path of thermal flow between the fluid streams passing through the exchanger. Valve 2 preferably is operated automatically so that the valve settings will cause the compressed air to flow pant of the time through line 4 and upwardly through passageway 6 of the exchanger. During the interval while the compressed air is passing through passageway 6, cold backward-returning nitrogen-rich product is passing downwardly through passageway 7 in countercurrent cold-exchange relationship with the air in passageway 6. The nitrogen-rich product thereupon leaves exchanger 3 through line 5, reversing valve 2 and is exhausted into the atmosphere through line S. After an interval of time the setting of valve 2 is reversed and the compressed air caused to flow `through passageway 7. At .this time the nitrogen-rich product ows downwardly through passageway 6 and is vented to the atmosphere through line 4, valve 2 and line 8. In addition xto the cooling etfect obtained from the nitrogen-rich product, the compressed air receives additional cooling elect from fthe backward-returning oxygen product stream that is passing continuously through the inner passageway 9 of exchanger 3, the direction of llow of the latter stream necessarily being always countercurrent to the flow of the compressed air.

The temperature of the air during its passage through exchanger 3 is reduced progressively to about minus 150 -completely free of carbon dioxide.

. I 5 to minus 162 F. and this causes the residual amounts of water vapor which entered the exchanger with the compressed air to be precipitated as liquid and/or frost upon the metal surfaces of its passageway. Substantially anhydrous air leaves exchanger 3 either through line 10 or line 11, depending upon the phase of the reversing cycle, and is conducted therethrough into either passageway 12 or 13 of reversing exchanger 14. This latter exchanger is constructed similarly to exchanger 3 and its several passageways likewise function similarly to the corresponding passageways of exchanger 3. Exchanger 14 does not necessarily need to be a separate vessel and optionally may be a continuation of exchanger 3 having its passageways as extensions of the corresponding passageways of exchanger 3.

. During its passage through exchanger 14 the temperature of the compressed air is lowered further to a degree below that at which carbon dioxide precipitates but which is above the dew-point of the air. Pursuant to present embodiment of the invention, approximately 10% of the compressed air is diverted from the main stream passing through the exch-angers and is taken away by line 1S or 16, having check valves 17 and 18 respectively, depending upon whether the ow of the compressed airis through line 10 or 11 in accordance with the phase of the reversing cycle. The diverted portion of the air is then passed through line 19, having valve 22, into the lower section 23 of filter vessel 24. Meanwhile, the remaining 90% portion of the compressed air continues through exchanger 14 in cold-exchange relation with the nitrogenrich product and thereby has its temperature reduced to about minus 268 F. At this temperature the compressed air leaves the exchanger by way of either line 25 and check valve 26 or line 27 and check valve 28, again depending upon the particular phase of the reversing cycle. ln either event the compressed air finally is passed through valved line 29 and is introduced therethrough also into lower section 23 of filter vessel 24. This section serves as a mixing zone and the diverted and undiverted portions of the compressed air are thoroughly commingled with a resultant temperature reduction of the diverted portion to a degree which is below the solidication temperature of its carbon dioxide content. Consequently, carbon dioxide is precipitated therefrom and carried as a suspension of solids in the total compressed air stream. While some of the solid particles settle by gravity to the bottom of the mixing zone, the majority of the particles are conveyed with the air through perforated baffle 30, whose function is to provide complete mixing of the two streams before the filtering step, into the filter section 31 of vessel 24. A hollow cylindrical iilter element 32, comprising as the filter means glass cloth, porous stone, Porex, etc., projects into section 31. The compressed air, leaving the solid particles of ycarbon v dioxide on the walls of the tilter element passes into the central space behind the walls and thereafter leaves vessel 24 by way of line 33, havingvalve 34, substantially Two or more filtering vessels similar to vessel 24 may be employed for the filtering step so as to permit alternate switching of the vessels E the line for cleaning. If desired, the solid particles of carbon dioxide may be removed from the compressed air by means of cyclone separators. An auxiliary by-pass or blow-back line 35, having valve 36 is interposed between lines 19 and 33 and may be used for passing compressed air in reversed direction through a fouled lter to clean it. In this event, the air used for cleaning the filter may be vented through the valved vent line 3'7.

The purified and cooled compressed air leaves vessel 24 through line 33 at a temperature of about minus 253 F. and once more is divided into two portions. The larger portion, which in the present instance represents approximately 59% of the air stream, continues to passy through line 33 to liqueiier vessel 38 for cold-exchange relation with the nitrogen-rich product. The air, being under a superatomspheric pressure, preferably is conducted through coil 39 around the liqueer While the nitrogen-rich product, since it is under a lower pressure, is passed through the shell of the liqueer. To provide for eiicient thermal flow liqueer 38 may also be packed with a metallic packing and this packing bonded to the inner walls of the vessel, or otherwise constructed. Likewise coil 39 is metal bonded to the exterior wall of vessel 38 and for the same reason. The cold-exchange relation obtained in vessel 38 causes a further reduction in the temperature of the air to about minus 274 F. and this low temperature elects partial condensation of the compresssed air to an extent of about 10%. The thus partially condensed air leaves the liquefier through line 4t) and the interposed valve 41 and is conducted therethrough into the bottom of the high pressure section 42 of fractionator 43.

Returning now to the portion of compressed air which is diverted from line 33, this portion which -amounts to 41% of the total air passing through line 33 is taken through line 44 and control valve 45 and injected into expander engine 46. In the expander the pressure of this portion of the compressed air is reduced with the performance of work to about l0 pounds per square inch gauge and its temperature correspondingly is lowered to approximately minus 304 F. In this expanded condition the diverted portion of the air is taken from the expander through line 47 and introduced as vapor feed into the low pressure section 48 of fractionator 43. A knockout drum may be placed in line 47, if desired, to facilitate the starting-up operation and to remove any residual impurities in the expanded air.

Returning now to aconsideration of what occurs in the high pressure section 42 of the fractionator, the vaporous part of the compressed air from line 40 rises upwardly through the several vapor-liquid Contact trays 49 and thus is brought into contact with a liquid reux formed by condensation in the top of this section. This contact effects a bottoms product rich in oxygen and a top product which is practically pure varporous nitrogen. Vapors of nitrogen rise upwardly into the condensing tubes of calandria 5t) which, being immersed in a body of boiling liquid oxygen at minus 288 F. serves as the reboiler for the low pressure section 48 by obtaining the necessary heat for reboiling from condensation of the nitrogen vapors. Liqueed nitrogen at minus 282 F. returns from the Calandria into the top of high pressure section 42 Where a part is collected on an upper tray and the remainder is caused to cascade downwardly over trays 49 as the reux liquid. In descending over trays 49 the liquid nitrogen absorbs heat to condense the rising vapors of air and the greater portion thereof is revaporized. The oxygen-rich liquefied air resulting from the fractionation accumulates in the base of section 42.l at a temperature of about minus 272 F.

A portion of this liquid is withdrawn continuously through line 51, passed through iilter 52 and line 53, having valve 55, to an expansion valve whereupon it is expanded through expansion valve 57 into an intermediate part of the low pressure section 48 of fractionator 43. It is the function of iilter 52 to remove any residual particle of solid carbon dioxide which may have advanced thus far in the system. Duplicate vessels similar to filter 52 may be employed to permit removal of -a fouled lter element for cleaning.

Simultaneously With the introduction of the oxygen enriched liquefied air to the low pressure section 48, liquefied nitrogen likewise is withdrawn from the high pressure section and caused to ow through line 60, having Valve 62, to the low pressure section whereupon it is introduced into the top of section 48 through expansion valve 64. As stated heretofore, vaporous air under low pressure is introduced into section 48 of the fractionator from line 47. These vapors are contacted at this low pressure with the liqueed 'constituents expanded into this section of thepfractionator through expansion valves-57 and 64. Rectification occurs on the several vapor-liquid Contact trays 65 of this section whereby a nitrogenrich vaporous product is taken overhead from this section and a substantially ypure oxygen product is accumulated as a liquid bottoms `product surrounding Calandria Si?. Revaporization of: liquefied oxygen, as the result of condensing nitrogen vapors in the Calandria, provides for the vapor reflux in section 48. At times it may be necessary to reject from the system a small part the liquecd oxygen accumulated in the base of the low pressure sec tion 48. This is done by opening valve 5S in the drain line 59. from section 48 at a point immediately above the level of the liquefied oxygen surrounding Calandria Sti and passed through line ,66 to the innermost passageway 67 oli` cold exchanger 14. The oxygen vapors are subsequently warmed to approximately 91 F. by passage through cxchanger 14, line 68 and passageway 9 of exchanger 3. The warmed oxygen is then removed as a pure product of the process Vthrough line 70.

Simultaneously with the removal of oxygen vapors from the fraetionator, nitrogen vapors are taken overhead through line 71 at a temperature of about minus 311 F. and at a pressure of about l pounds per square inch gauge. ln the present example these vapors ow through line 7l, having valve 72 to liqueiier 38 for countcrcurrent cold-exchange relation with the portion of cornpressed air as heretofore described. In the event that all of these vapors are not required to provide for the cold exchange necessary to reduce the temperature of the compressed air flow through line 40 to about minus 274 F., a portion ot the nitrogen vapors may be by-passed around 'liquefier 4t) through line 73, having valve 74, and rejoin the nitrogen vapors leaving the liquefier through line 75. The now combined total nitrogen-rich product stream, which has been warmed by the heat exchange with warmer air to a temperature of about minus 275 F., is conveyed through line to the check valve manifold system controlling thc fluid flow into the cold end of exchanger 14. During the interval when valve 2 has been operated to cause the compressed air to flow through passageways 6 and k12 of exchangers 3 and 14 respectively and to leave the latter exchanger by way of line 25 and check valve'26, the mechanism of the checl: valves cause the backward-returning nitrogen-rich product to ilow through check valve'76 into line 27 and through passageways 13 and 7 of exchangers 14 and 3 respectively. After its passage through the exchangers the nitrogen product is vented from the system through line 5, reversing valve `2 and line 8 at a temperature of about 9i F. During the reversed phase of the operation of the exchangers when valve 2 is actuated to cause the compressed air to tiow through passageways? and 13 and to leave the latter passageway through line 27 and check valve 28, the mechanism of the check valves will automatically actuate themselves to permit the nitrogen-rich product to flow l'rom line 75 through check valve 77 into `line 25 for passage throngh passageways 12 and 6 of exchangers 14 and 3 respectively. In this event, the nitrogen-rich product is vented to the atmosphere from the latter passageway through line 4, reversing valve 2 and line 3.

ln the event that the expander eiliciency is high enough to require an inlet temperature so wann that the com- A portion of the oxygen vapors are removed portion of the compressed aiuto a temperature that will Aprevent the formation of liquid air inthe expander engine.

'Referring to the drawing `of Figure 2, and particularly to the compressed `air flowing through lines 10 or 11 according to the phaseof the reversing cycle, in the present modilication approximately 6% of the air compressed to about 85 pounds per square inch is diverted from the main stream through lines and 16. The thus diverted portion is then carried through line to cold exchanger 7f3, valve `79 being suitably adjust-ed for proper liow con* ditions. Cold exchanger 78 is utilized for the purpose of extracting heat from this portion of the compressed air with no precipitation of carbon dioxide as shall be explained hereafter. From exchanger 78 this portion ofthe air passes through line 21 at a somewhat lower temperature and is introduced therethrough into the lower section 23 of filter vessel 24. vThe remaining 94% portion et the compressed air continues its passage through either line itl or 1i and exchanger 14 whereby its temperature is reduced to about minus 266 F. with resultant carbon dioxide precipitation. This portion likewise is introduced into section 23 of the filter vessel to be thoroughly cornmingled therein with the smaller aforementioned diverted portion. The temperature of the recombined streams of air reaches approximately minus 261 F. and

at this temperature the remaining carbon dioxide is precipitated and carriedas a suspension of solids in the air into filter section 3l. of vessel 2-'-l. Filtered air, substantially free of carbon dioxide, leaves vessel 24 through line 33 but since it is at a temperature in the neighbor hood of minus 261 F. the air at this temperature cannot be expanded in the expander engine without being at least partially condensed to the liquid phase. Therefore, for the purpose of raising the temperature to a degree suffi ciently high to prevent the occurrence of condensation. this air is passed through cold exchanger 78 by way of line 81, valvei8-2 being opened. It is thus brought into heat-exchange relation with at least part of the diverted 6% portion of the compressed air which passes into and out of exchanger 78 by way of lines 2t) and 21 respectively whereupon the air leaving heat exchanger 78 through line 33 is warmed to about minus 235 F. Valved line serves as a by-pass line for temperature control purposes in exchanger 78. At this temperature the thus warmed air is passed to expander 46 from the exchanger by way or line 83. When the air is subsequently expanded with the performance of work in expander 46 to a reduced pressure of about l() pounds per square inch gauge no condensation of liquid air occurs so that dry expanded air passes through line 47 at a tcm perature of about minus 304 F. for introduction into the `low pressure section 48 of fractionator 43 as the vapor `ot the fractionator to produce an oxygen-rich liquid bottoms product and a substantially pure liquefied nitrogen top product.

The liquefied oxygen-rich product, which has collected in the base of the high pressure section 42 of the fractionator, 'is withdrawn in a continuous stream through line 5l,

`passed through filter 52, and introduced into subcooler 69 by way of line 53, valve 83 being opened. ln subcooler 69 this stream is further cooled by cold exchange with the-product nitrogen vapors to such an extent that when it is thereafter expanded into the fractionator throughvalvei57 in line 56 there is no excessivevaporization of this liquid. Simultaneously with the passage of the oxygenuich liquid through the subcooler, the liquefied nitrogen top product from section 42 is removed from an upper tray of section 42 and passed through line 60 to subcooler 84, valve 85 being opened. The stream of this product likewise is subcooled in subcooler 84 by the cold vapors of nitrogen effluent from the top of fractionator 43 to prevent excessive flashing of this material as it also is expanded into the top of section 48 through exp'ansion valve 64 after passage through line 63. Rectification of the vaporous air from expander 46 and the components expanded through valves 57 and 64 tak-es place at the reduced pressure existing in section 48. The liquid bottoms product of this rectification, being substantially pure oxygen, accumulates as a pool of liquid surrounding the tubes of Calandria 5 0. Vaporization of the liquefied oxygen occurs as the result of condensing nitrogen vapors within the tubes of this -cal-andria and supplies the vapor reflux for section 4S. A portion of the thus formed oxygen vapors are removed from the fractionator at a point immediately above the level of the pool of liquefied oxygen `and taken from the system in the manner stated heretofore. The vaporous nitrogen overhead product of the rectification is taken from fractionator 43 at a temperature of about minus 311 F. through line 86, valve 87 being opened, to subcooler 84. Having been warmed somewhat in subcooler 84 by subcooling the liquefied pure nitrogen, these vapors -of nitrogen pass immediately to subcooler 69 by way of line 88 wherein they again impart some of their cold to effect subcooling of the oxygen-rich liquid passing through the shell side of this subcooler. The thus further warmed stream of nitrogen vapors leave subcooler 69 through line 89, to liquefier 38,

The foregoing illustrative examples describe processing arrangements wherein the oxygen-rich product is recovered lin the vapor phase. Itis to be understood, however, that this product optionally may be recovered lin the liquid phase and in this event the aforedescribed operating conditions necessarily will have to be readjusted to meet the change of refrigeration requirements imposed on the system. V l

It `is to be understood further that my invention is not to be limited to any of the embodiments described herein for illustrative purposes but only in and by the following claims.

I cla-im:

l, An apparatus for separating a gas mixture into output components including in combination a cold-exchanger consisting of lat least two iiuid conduits connected in operative cold exchange relation to effect cooling of a. compressed gas mixture by countercurrent cold exchange with at least one of the cold expanded output `components Iof the separation, means for conducting a compressed gas mixture to either of said fluid conduits, means for separat-V ing and removing a portion of the compressed gas mixture from said cold-exchanger at a point intermediate the ends thereof, a fluid mixing chamber, a iiuid conduit connecting between said means for separating and removing a portion of the compressed gas mixture and said mixing' chamber, another fluid conduit for conducting the remainder of said gas mixture from the cold endof said.. cold-exchanger to said mixing chamber, means. for remov ing solid precipitated vapors from `said gas. mixture, a. fluid transfer means connecting in yoperative relation said mixing chamber and' said solids removal means, a gas expanding means, a iiuid conduit .connect-ing said gas: expanding means and said solids removal means, a heat. exchanger disposed in said last-mentioned iiui-d conduit and -connected in operative relation with said fluid conduit; connecting between said means for `separating' and removing a portion of the compressed gas mixture from said cold-exchanger end said mixing chamber for warming gas. passing through the former conduit by heat exchange with gas passing through the latter conduit, means for liquefying and rectifying a gas mixture into higher and lower boilavvenne f ing output components, conduits connecting in operativex Y 10` relation said last-mentioned means with said gas expand-l ing means and said solids removal means for passing gases therethrough from the latter to the former means, conduits having their origin in said means for liquefying and rectifying a gas mixture at least one of which connecting with `said cold-exchanger for passing out of the output components of the separation therethrough in Iits vapor phase, means for passing `said one of the output components to either of said two fluid conduits `connected in -operative cold exchange relation in said cold-exchanger, valve .means for controlling flow `of said compressed gas mixture and said one of the output components through the fluid conduits in said cold-exchanger and means for periodically so changing the valve means as to inter-change the flow of the compressed gas mixture and said one of the output components between said Huid conduits in said cold exchanger.

2. An apparatus for separating a gas mixture intoy output componen-ts including in combination a cold exv changer consisting of iiuid conduits connectedin opera tive cold exchange relation to effect cooling of a com-4 pressed gas mixture by countercurrent cold exchange with at least one of the cold expanded output components ofl the separation, conduit means connecting a source of' the compressed gas mixture and at least two of said uid end of said cold exchanger to said chamber, a means forv removing solid precipitated vapors from said gas mix-- ture, a liuid transfer means connecting in operative relation said chamber and said solids removal means to trans- -fer solids-containing gas mixture from the chamber to the solids removal means, a means for liquefying and rectifying a gas mixture into higher and lower boiling components, a uid conducting means connecting said solids removal means and said liquefying and rectifying means for conducting outflowing solids-free gas mixture from the said removal means to the rectifying means, a gas expanding means, a fluid conduit connecting between the compressed gas inlet of said gas expanding means and the said fluid conducting means for passing a portion of the solids-free gas mixture being conducted through said iiuid conducting means to the gas expanding means, a fluid conduit connecting the gas outlet of said gas expanding means and said liquefying and rectifying` means for conveying expanded gas mixture therethrough` from the formed to the latter means, tubular conduits.

having their origin in said means for liquefying and rec tifying, one of which connecting operatively with theV cold end of each of said firstfmentioned two iiuid con-- duits in said cold exchanger, for passing output com ponents of said gas mixture from said liquefying and rectifying means therethrough, valve means in said one of the tubular conduits connecting with said iirst-men tioned two tiuid conduits for alternately passing one of the output components to one of said two fluid conduits while simultaneously excluding delivery of said output component to the other, means for actuating both said mentioned valve means cooperatively thereby simultaneously directing flow of said compressed gas mixture and said one of the output components through one of said two fluid conduits in said cold exchanger and periodically changing the valve means as to interchange the tflow of the compressed gas mixture and said one of the output components alternately between said two fluid conduits in said cold exchanger.

3. In the method for separating a mixture of gases having diterent boiling points in the liquid state, 'cornprising passing such a gas mixture in a compressed condition through a path in a heat exchange zone wherein the gas mixture is cooled, passing an output component of said separation under low temperature and pressure than said compressed gas mixture through another path in said zone in countercurrent heat exchange relation with said gas mixture and periodically interchanging the flow of the gas mixture and said output component in said paths, each of the gas mixture and output component passing through the Zone always in the same direction as the initial flow thereof irrespective through which of said paths it is flowing so that, by reason of the countercurrent relationship between the gas mixture and output component, each said interchange reverses the direction of fluid flow in each of said paths; the improvement which comprises separating said gas mixture into two parts prior to its complete passage through said Zone, removing the first of said parts `directly from said zone, continuing the passage of the second part through said zone, further cooling the gas mixture in said second part to a temperature sufficient to substantially completely precipitate and deposit a higher boiling constituent of the gas mixture in a colder portion of said zone, removing the further cooled said second part from the heat exchange zone, commingling both of said parts of the gas mixture, whereby the Viirst part is cooled suh'iciently by said further cooled second part to at least said precipitation temperature to precipitate substantially completcly therefrom the said higher boiling constituent, removing the precipitate from the commingled parts of said gas mixture, separating the gas mixture substantially free of said higher boiling constituent into output components by liquefaction and rectification under a lower pressure and then passing one of said output components at said lower pressure through a path in said heat exchange zone and over deposits of precipitate therein as said output component in countercurrent heat exchange relation with the gas mixture, whereby said output component substantially completely evaporates and removes precipitate deposited in said colder portion during the next preceding period before interchange of the paths of the gas mixture and said output component.

4. The method in accordance with claim 3 wherein said mixture of gases is air, said output component is predominantly nitrogen and said higher boiling constituent of the gas mixture is carbon dioxide.

5. The method in accordance with claim 3 wherein said heat-exchange Zone has at least two separate parallel paths in heat exchange relation with each other, the compressed gas mixture being passed through one of said paths while the said output component is simultaneously passed through another of said paths.

6. in the method for separating a mixture of gases having different boiling points in the liquid state, comprising passing such a gas mixture in a compressed condition through a path in a heat exchange zone wherein the gas mixture is cooled, Jassing an output component of said separation under lower temperature and pressure than said compressed gas mixture through another path in said zone in countercurrent heat exchange relation with said gas mixture and periodically interchanging the ow of the gas mixture and said output component in said paths, each of the gas mixture and output component passing through the zone always in the same direction as the initial how thereof irrespective through which of said paths it is flowing so that, by reason of the countercurrent relationship between the gas mixture and output component, each said interchange reverses the direction of fluid how in each of said paths; the improvement which comprises separating said gas mixture into two parts prior to its complete passage through said zone, removing the first of said parts directly from said zone, continuing the passage of the second part through said zone, cooling said second part to a temperature sufiicient to substantially completely precipitate and deposit a higher boiling constituent of the gas mixture in a colder portion of`said zone, further cooling the precipitate-free second part below said precipitation temperature, removing the further cooled said second part from the heat exchange zone, commingling both of said parts of the gas mixture, whereby the rst part is cooled suiiiciently by` said further cooled second part to at least said precipitation temperature to precipitate substantially completely therefrom the said higher boiling constituent, removing the precipitate from the commingled parts of said gas mixture, separating the gas mixture substantially free of said higher boiling constituent into output components by liquefaction and rectitication under a lower e' re and then passing one of said output components t id lower pressure through a path in said heat exchange zone and over deposits of precipitate therein as said output component in countercurrent heat exchange relation with the gas mixture, whereby said output component substantially completely evaporates and removes precipitate deposited in said colder portion during the next preceding period before interchange of the paths of the gas mixture and said output component.

7. In the method of separating a mixture of gases having diterent boiling points in the liquid state, comprising passing such a gas mixture in a compressed condition through a path in a heat exchange zone wherein the gas mixture is cooled, passing an output component of said separation under lower temperature and pressure than said compressed gas mixture through another path in said zone in countercurrent heat exchange relation with said gas mixture and periodically interchanging the iiow of the gus 'mixture and said output component in said paths, each of the gas mixture and output component passing through the zone always in the same direction as the initial flow irrespective through which of said paths it is flowing so that by reason of the countercurrent relationship between the gas mixture and output component, each'said interchange reverses the direction of iiuid flow in each of said paths; the improvement which comprises separating said gas mixture into two parts prior to its complete passage through said zone, removing the first of said parts directly from said zone, continuing the passage of the second part through said zone, further cooling the gas mixture in said second part to a temperature sufficient to substantially completely precipitate and deposit a higher boiling constituent of the gas mixture in a colder portion of said zone, removing the further cooled said second part from the heat exchange zone, commingling both of said parts of the gas mixture, whereby the first part is cooled suticiently by said further cooled second part to at least said precipitation temperature to precipitate substantially completely therefrom the said higher boiling constituent, removing the precipitate from the commingled parts of said gas mixture at substantially said precipitation temperature, separating the gas mixture substantially free of said higher boiling constituent into output components by liquefaction and rectification under a lower pressure and then passing one of said output components at said lower pressure through a path in said heat exchange zone and over deposits of precipitate therein as said output component in countercurrent heat exchange relation with the gas mixture, whereby said output component substantially completely evaporates and removes precipitate deposited in said colder portion during the next preceding period before interchange of the paths of the gas mixture and said output component.

8. In the method for separating a mixture of gases having different boiling points in the liquid state, comprising passing such a gas mixture in a compressed condition through a path in a heat` exchange zone wherein the gas mixture is cooled, passing an output component of said separation under lower temperature and pressure than said compressed gas mixture through another path in said zone ign countercurrent heat exchange relation with t, i3 said gas mixture and periodically interchanging the ilow of the gas mixture and said output component in said paths, each of the gas mixture and output component passing through the zone always in the same, direction as the initial ilow irrespective through which of said paths it is flowing so that, by reason of the countercurrent relationship between the gas mixture 4and output component, each said interchange reverses the direction offuid flow in each of said paths; the improvement which comprises separating said gas mixtureinto two parts prior to its complete passage through said zone, removing the first of saidV parts directly from said zone, continuing the passage of the second part through said zone, further cooling the gas mixture in said second part to a temperature suiicient to substantially completely precipitate and deposit a higher boiling constituent of ythe lgas `mixture in a colder portion of said zone, removing the further cooled said second part from the heat exchange zone, commingling both of saidparts of the gas mixture, whereby the iirst part is cooled suiiciently by said further cooled second part to at least said precipitation temperature to precipitate substantially completely therefrom the said higher boiling constituent, ltering the precipitate fromthe commingled parts of said gas mixture at substantially said precipitation temperature, separating the gas mixture substantially free of said higher boiling constituent into output cornponents by liquefaction and rectification under a lower pressure and then passing one of said output components at said lower pressure through a path in said heat exchange'zone and over deposits of precipitate therein as said output component in countercurrent heat exchange relation with the gas mixture, whereby said output component substantially completely evaporates and removes precipitate deposited in "said colder portion during the next preceding period before interchange of the paths of the gas mixture and said output component.

9. In the methodfor'separatingv a mixture of gases having dilerent boiling points in their liquid state comprising passing a stream of such 'a gas mixture in a compressed'condition through a path in a heat exchange zone wherein the gas mixture is cooled, passing a gaseous stream of output component of said gas mixture under lower temperature and pressure than said rst stream through another path in said zone in countercurrent heat exchange relation with said first stream and periodically interchanging the flow of the two streams between said paths, the flow of the respective streams being always in the same direction as their initial iiow through said zone so that by reason of the countercurrent relationship between the two streams each said interchange reverses the direction-of uid flow in each of said paths; the improvement which comprises separating said iirst stream into two unequal parts prior to its complete passage through said zone, yremoving the smaller of said parts directly from saidr zone, continuing the passage of the larger of said parts through said zone, regulating the respective flows of said larger part and said stream of output productsthrough said zone so that the temperature within a colder portion thereof is controlled to effect substantially complete precipitation and deposition of a condensible constituent from .said larger part of said. rst Stream and the temperature difference between said larger part of the first stream leaving and said second stream entering the colder portionof said zone is within the range of about 5-l0 F., removing said larger part of the first mentioned stream from said heat exchange zone, commingling both said smaller and larger parts of said first stream whereby the smaller of said parts is cooled suiciently by the larger part to eiect substantially completely therefrom the precipitation of said condensible constituent, removing the precipitate from the commingled parts of said iirst stream, passing the components of the condensible-free said rst stream to a liquefying and rectifying step under lower pressure to separate the gas mixture into output components, effecting said last avvisati 14 mentioned separation, removing from said rectifying step a gaseous stream rich in the lowest boiling component of said gas mixture and passing the last mentioned stream at said lower pressure through a path in said heat exchange zone and over precipitated deposits therein as the said second gaseous stream in countercurrent heat exchange relation with said rrst stream whereby upon each of said interchanges the said second gaseous stream substantially completely evaporates and removes precipitate deposited in said colder portion of said zone during the next preceding period before interchange of paths of said rst and second streams through said zone.

l0. In the method for separating air, having water vapor and carbon dioxide as impurities, comprising passing the air in a compressed condition through a path in a heat exchange zone wherein the air is cooled, passing the nitrogen-rich output product of the separation under lower temperature and pressure than the air through another path in said zone,f effecting a countercurrent heat exchange relation between said output product and com pressed air and periodically interchanging the iiow of air and output product in said paths, each of the air and output product passing through the zone always in the same direction as the initial flow irrespective through which of said'paths it is flowing so that, by reason of the countercurrent relationship between the air and output product each said interchange reverses the direction of fluid iiow in each of said paths; the improvement which comprises passing the compressed air continuously through a first stage of said zone, cooling the air to a temperature sulicient to elect substantially the complete precipitation and deposition of the water vapor, withdrawing the cool and water-free air from said first stage, separating the withdrawn air into two unequal parts, removing the smaller of said parts directly from said zone, passing the larger of said parts through a second stage in said zone, further cooling the air in said second part to a temperature sutiicient to substantially complete ly precipitate and deposit the carbon dioxide impurity in a colder portion of said zone, withdrawing the further cooled said second part from said second stage of the heat exchange zone, commingling the said smaller with said larger part of the air whereby the smaller of said parts is cooled'suiiiciently by said further cooled larger of said parts to at least Said precipitation temperature of carbon dioxide thereby eiecting precipitation of the carbon dioxide impurity from the smaller of said parts, removing said last mentioned precipitate from the commingled parts of the air at said carbon dioxide precipitation temperature, separating the substantially impurityfree air into oxygen-rich and nitrogen-rich output products by liquefaction and recitiication under a pressure lower than that imposed on said compressed air, recovering said output products of recitilication and passing the nitrogen-rich product'at said lower pressure through a path in said heat exchange zone and over deposits of precipitate therein as the said nitrogen-rich output product of the separation effecting countercurrent heat exchange relation. with the compressed air whereby the nitrogen-rich output product substantially completely evaporates and removes precipitated impurities deposited in said zone during the next preceding period before interchange of the paths of air and said nitrogen-rich output product. i

ll. In the method for separating a mixture of gases having different boiling points in the liquid state, comprising passing a stream of such a gas mixture in a cornpressed condition through a path in a heat exchange zone wherein the gas mixture is cooled, passing a stream of output products of said separation under lower temperature than said compressed gas mixture through another path in said zone in countercurrent heat exchange relation with said stream of gas mixture f and periodically interchanging the ow of said streams through said paths, `of the respective streams passing through said zone always iny the same direction; as the initial flow thereof irrespective through which of said paths' it fis flowing the improvement which comprises separating said stream of gas mixturefinto two parts priorto its complete passage throughsad zone,l withdrawing the first of said'parts directly from said zone, continuing the passage of the second of said parts through saidzone, further cooling the gas mixture insaid second part to a temperature sufficient to substantially completely precipitate and deposit a high boiling constituent thereof in a colderportionfof said zone, withdrawing the furthercoole'd said second part from said zone, commingling both of said parts to cool said first of said parts t`o` said precipitation temperature thereby effecting substantially the complete precipitation of the said higher boiling constituent 'of the"y gas mixture from said commingled parts, removing said last mentioned precipitate from the commingledparts of the stream of gas mixturey at said precipitation temperature, dividing the precipitate-free stream of gas mixture into two fractional parts, expanding the first of said fractional parts to lower pressure with the performance of external work, subsequently subjecting both of said fractional parts to a commonliquefac'tion and rectification step at said lower pressure toseparate the gas mixture into output products, recovering output products from the rcetifying separationand passing a stream rich in one of said output products through a path in said heat exchange zone and over deposits of Iprecipitate therein as said second mentioned stream of output products in countercurrent heat exchange relation with the llrstmentioned stream of compressed gas mixture whereby said stream of output products substantially completely cvaporates and removes precipitate deposited in said colder portion during the next preceding period before` interchange of the paths of the streams of gas mixture and said output products.

` l2. The method in accordance with claim 1l wherein the first of the fractional parts divided from the precipitate-free stream of gas mixture is warmed before the expansion thereof with the performance of external work by being subjected to a separate heat exchange relation with at least a portion of the first part separated from thc stream of compressed gas mixture prior to the cornplete passage of said stream through the heat exchange zone, after direct withdrawal of` saidrst separated part from said :fone but before subsequent commingling thereof with the cooled and precipitate-free second` of said` said gas mixture is predominantly nitrogen and said` higher boiling constituent of the gas mixture is carbon dioxide.

t4. The method in accordance with claim ll wherein the first of the fractional parts divided from the precipitate-free stream of gas mixture is warmed before the expansion thereof with theperformanee of vexternal work.

l5. In the method of treating a mixture of gases, containing a higher boiling component as an impurity, wherein a stream of compressed gas mixture is passed in one direction of flow through a reversing heat exchange zone in heat exchange with relatively cool counterllowing fluid, obtained from the gas mixture in a latter stage of treat- Cit 1r? ment and not greater in mass quantity than the gas mixture, along a path in the heat exchange zone progressively decreasingV in temperature from end to end to effect cooling of the gas mixture and resultant precipitation of said higher boiling componentin `a colder portion of said path, and wherein a second gaseous stream comprising at least a portion of said counterilowing fluid and `substantially free of the higher boiling 'component and at lower temperature than Vsaid colder portion is passed subsequently through the same pathin the" opposite direction of flow after' the first stream has ceased tlow therein; the step of controlling the temperatureV of said colder portion of saidl path by divertinga minor portion of said stream of compressed gas mixture from the heat exchange zone before the streamreaches said colder portion, passing the major portion of compressed gas mixture through said colder portion of the heat exchange Zone, further cooling the major portion flowing through the colder portion Vof the heat exchange `zone `to a lower temperature level than the temperature level `of said colder portion produced by `said first-mentioned heat exchange by passing said major portion in heat exchange with counterflowing lluid` greater in mass quantity than the gas mixture in the major portion `to maintain a difference between the temperature at which said precipitation occurs at any point in 'said colder portion and the temperature at which said second gaseous stream flows pastrsaid point which is less than would exist but for the diversion of said minor portion, removing the further cooled major portion of compressed gas mixture from the heat exchange zone, then recombining the portions of said stream of compressed gas vmixture to cool the minor portion and cause` precipitation of said higher boiling impurity therefrom. i

16. Apparatus for reversing heat exchange` between a gas mixtu'rein compressed condition `and a less cornpressed cooling fluid including in combination a reversing heatexchanger comprising yat least two fluid paths connected inoperative countercurrent heatexchange relation, inflow conduits for Yrelatively warm gas mixture and relatively cold cooling fluid, outflow conduits for cooled gas mixture and warmed cooling fluid, directive conduit means connecting each of the gas mixture inflow conduit and the coolingoutflow conduit with -thewarm ends of both of said paths, directive means connecting each of the gas mixture outflow conduit and the cooling fluid inflow conduit with the cold ends of both of said paths, valve means inueach of saidhdirective conduits for c ontrolling llow of the gas mixture and cooling fluid to and through said paths, a fluid mixing means, means for separating and removing a portion of the gas mixture from either of said pathsat` a point intermediate'the ends thereof, conduit means connecting lbetween the last-mentioned means and the lluid mixing means, and means connecting between the cooled gas mixture outflow conduit and the fluid mixing means whereby partially cooled gas mixture is conducted from an intermediatepoint ofone oftsaid paths and recombined with colder gasmixture in the uid mixing means.

References Cited in the file of this patent UNITED .STATES` PATENT S` 

1. AN APPARATUS FOR SEPARATING A GAS MIXTURE INTO OUTPUT COMPONENTS INCLUDING IN COMBINATION A COLD-EXCHANGER CONSISTING OF AT LEAST TWO FLUID CONDUITS CONNECTED IN OPERATIVE COLD EXCHANGE RELATION TO EFFECT COOLING OF A COMPRESSED GAS MIXTURE BY COUNTERCURRENT COLD EXCHANGE WITH AT LEAST ONE OF THE COLD EXPANDED OUTPUT COMPONENTS OF THE SEPARATION, MEANS FOR CONDUCTING A COMPRESSED GAS MIXTURE TO EITHER OF SAID FLUID CONDUITS, MEANS FOR SEPARATING AND REMOVING A PORTION OF THE COMPRESSED GAS MIXTURE FROM SAID COLD-EXCHANGER AT A POINT INTERMEDIATE THE ENDS THEREOF, A FLUID MIXING CHAMBER, A FLUID CONDUIT CONNECTING BETWEEN SAID MEANS FOR SEPARATING AND REMOVING A PORTION OF THE COMPRESSED GAS MIXTURE AND SAID MIXING CHAMBER, ANOTHER FLUID CONDUIT FOR CONDUCTING THE REMAINDER OF SAID GAS MIXTURE FROM THE COLD END OF SAID COLD-EXCHANGER TO SAID MIXING CHAMBER, MEANS FOR REMOVING SOLID PRECIPITATED VAPORS FROM SAID GAS MIXTURE, A FLUID TRANSFER MEANS CONNECTING IN OPERATIVE RELATION SAID MIXING CHAMBER AND SAID SOLIDS REMOVAL MEANS, A HEAT EXPANDING MEANS, A FLUID CONDUIT CONNECTING SAID GAS EXPANDING MEANS AND SAID SOLIDS REMOVAL MEANS, A HEAT EXCHANGER DISPOSED IN SAID LAST-MENTIONED FLUID CONDUIT AND CONNECTED IN OPERATIVE RELATION WITH SAID FLUID CONDUIT CONNECTING BETWEEN SAID MEANS FOR SEPARATING AND REMOV- 